This invention relates to wellbore slickline electric cables, and methods of manufacturing and using such cables. In one aspect, the invention relates to a method of manufacturing wireline composite slickline cables.
Generally, geologic formations within the earth that contain oil and/or petroleum gas have properties that may be linked with the ability of the formations to contain such products. For example, formations that contain oil or petroleum gas have higher electrical resistivity than those that contain water. Formations generally comprising sandstone or limestone may contain oil or petroleum gas. Formations generally comprising shale, which may also encapsulate oil-bearing formations, may have porosities much greater than that of sandstone or limestone, but, because the grain size of shale is very small, it may be very difficult to remove the oil or gas trapped therein. Accordingly, it may be desirable to measure various characteristics of the geologic formations adjacent to a well before completion to help in determining the location of an oil- and/or petroleum gas-bearing formation as well as the amount of oil and/or petroleum gas trapped within the formation.
Logging tools, which are generally long, pipe-shaped devices, may be lowered into the well to measure such characteristics at different depths along the well. These logging tools may include gamma-ray emitters/receivers, caliper devices, resistivity-measuring devices, neutron emitters/receivers, and the like, which are used to sense characteristics of the formations adjacent the well. A wireline cable, such as a slickline cable, connects the logging tool with one or more electrical power sources and data analysis equipment at the earth's surface, as well as providing structural support to the logging tools as they are lowered and raised through the well. Generally, the wireline slickline cable is spooled out of a drum unit from a truck or an offshore set up, over pulleys, and down into the well.
Slickline cables used in the oilfield industry typically consist of metallic tubes containing optical fibers or insulated copper conductors. The tubes are typically made of Iconel® which is non-corrosive, but is inherently low in strength. This lack of strength prevents these slickline cables from being used with much pull force. Because slickline cables have metallic tubes and are used with relatively small sheaves (16 to 20 in. in diameter) they are also prone to yielding and failure as they pass over sheaves.
Commonly, slickline cable designs use an epoxy/fiber composite sandwiched between two steel tubes with optical fibers contained in the inside tube. As shown in FIG. 1A, in some designs, optical fibers 102 (only one indicated) are placed in a central stainless steel tube 104. Epoxy/long fiber composite 106 is then pultruded over the tube 104, and an outer tube 108 is generally placed over the composite 106. The composite 106 provides a lightweight strength member as well as a hydrogen-resistant barrier for small, stand alone optical fiber conductors. But, as the long fibers in the epoxy/long fiber composite 106 and the metal forming the tubes 104 have significantly different thermal coefficients, the epoxy/long fiber composite 106 tends to deform during heat curing (at 400° to 500° F.) into a slightly irregular oval shape, as indicated by the gaps 110 (only one indicated) as shown in FIG. 1B. An outer stainless steel tube 108 is then drawn over the outside of the epoxy/long fiber composite 106. When the epoxy/long fiber composite 106 irregular profile resulting in gaps 110 is left uncorrected before applying the outer stainless steel tube 108, that tube 108 becomes especially vulnerable to failure during handling (for example at crossover points on drums, or when going over sheaves) and during operations in the field. Also, in some instances, loose fibers on the surface of the epoxy/fiber composite material 106 can build up at the entrances to extrusion tip and lead to jamming/interruption of the manufacturing process line.
One method of correcting the composite layer's 106 profile is to compression extrude a polymer layer over the composite layer before applying the outer steel jacket. This causes several problems. First, because the profile can be as much as 7 to 15 mil out of round, an equivalent amount of coating would be required, thereby increasing the line's diameter, and most often, there is no space available in slickline cables to allow for coatings of that thickness. Second, applying compression-extruded polymer over the epoxy/long fiber composite reheats the epoxy. This reheating releases moisture and other volatile residues causing blistering of the extruded polymer. Third, loose fibers or fuzz from the epoxy/fiber composite collect at the back of the tip of the extruder head due to fuzz build-up from the cured pultruded core. This leads to jamming at the tip of the extruder and cable breaks, which prevents long-length extrusions.
Also, in the manufacturing process, as illustrated in FIG. 2, three uncured rectangular “tows” 202 of epoxy/fiber composite are brought together over the inside steel tube 104 of FIG. 1, as tube 104 enters a pultrusion die. As each of the tows 202 is bent around the center metallic tube, the greatest tension occurs at the edges of the bent tow profile 204, causing the fibers to move toward the middle, to an area of lower tension. This causes each of the tows to distort as shown in 204. As a result, after exiting the pultrusion die over the inside steel tube 206 and contents thereof, the completed profile 208 of the epoxy/composite layer assumes a “cloverleaf” shape. Such a cloverleaf shade not only has significant variation in diameter about the periphery, but also varied domains of relative fiber/epoxy concentrations which may result in further weakening and making the cable less durable.
Thus, the need exists for reliable and efficient methods for manufacturing slickline cables consisting of an epoxy/fiber composite with improved circular profile consistency and distribution of fibers in the composite, and where the cable remains substantially round in cross-sectional shape while the cable is in use. Such a need is met at least in part by the following invention.